In interconnection in a semiconductor device, copper (Cu) is mainly used as a low-resistance interconnect material for forming interconnects (wiring lines) and vias (plugs).
In interconnect structures used in most advanced semiconductor devices, interconnects and vias are increasingly miniaturized. The miniaturization (scaling-down, shrinking) has presented the following problems in the interconnect structures: increased resistivity due to interfacial inelastic scattering of electrons, increased current density, and deteriorated reliability due to stress migration or electromigration.
Furthermore, in addition to the above problems, the size dependence of electrical resistance becomes noticeable along with the increasing miniaturization in a low-resistance interconnect material such as Cu that has a long mean free path.
Moreover, the interconnect using Cu has a damascene structure. Therefore, in addition to Cu as the interconnect material, a barrier metal film is formed in an interconnect trench (damascene trench) in which the interconnect material is embedded. As a result, an effective sectional dimension (sectional area) that contributes to the electrical conduction of the interconnect decreases as compared with the dimension of the formed interconnect trench.
In a DRAM, a flash memory, or a memory having a cross point structure, it may be preferable to use high-melting-point and low-resistance materials for a gate electrode and an interconnect of a transistor in regard to the manufacturing process of the above-mentioned memories.